Topic: 18volts at the battery terminal, is this possible??

[manjisann]

I foolishly had not been checking the fluid levels in my battery and a few days ago it let me know that was a mistake. I topped it back off and charged it, and took it into Batteries Plus and had them test it. They did a load test and everything and came back saying the battery is healthy.

I put it on my bike and started her up and I've been getting some really funky readings. At around 1500 rpms it's reading as high as a little over 18volts, but as I rev it up the voltage drops quite a bit and eventually goes to around 12.3 past 3000rpms. Is this possible? I did check the reg/rec last night and for some reason couldn't get a resistance reading when the meter was set to ohms, no matter which lead I stuck where (I was following the instructions in the clymer manual on how to test it) however if I set the meter to the diode setting I could get a reading of approx 500 (ohms?? not sure what that was measuring) one direction, switching the probes gave me a reading of infinite.

Every time I try to get new readings I get something weird. I'm beginning to suspect the DMM is fubar'd, it's a $4 Harbor Freight special. My question is, is it possible the DMM is reading correctly and there is something SERIOUSLY wrong with my charging system?

Thanks,

Brandon

[Silverback]

When R/Rs go bad they can overcharge, allowing too much voltage to the battery. Not sure what bike you are talking about but some R/Rs charge at idle until a certain RPM (5000 or so). Some R/Rs only charge at higher RPMs. Check that your volt meter is working first. Sounds to me like the R/R is bad and when you rev it the charging stops at a certain RPM giving you a non-charging battery reading. Could be why the sulfuric acid has boiled out of the battery also.

[TwoTired]

What bike?
Are all components stock?

[manjisann]

What bike?
Are all components stock?

Sorry, my bad. It's a 1980 CB650 Custom, stock electrical, only new age part is an electronic flasher relay. All connections are clean and coated with di-electric grease, I went through the entire harness and did this. Prior to the battery fluids going low at approx 1500 rpms the battery would measure at just below 12v and at around 3k rps it would shoot to 14.5 volts.

I'm really thinking it's the reg/rec that is shot, but I'm confused by the test results I've received. I'm fairly sure I am using the DMM correctly, but the results I've had are so varried that I'm just not confident of the results. We tested my friends R/R and it tested the same as far as not giving me a resistance value, yet we hooked it up and it's charging the battery properly.

Should I go and buy a new DMM from RadioShack?

Thanks guys,

Brandon

[cameron]

Prior to the battery fluids going low at approx 1500 rpms the battery would measure at just below 12v and at around 3k rps it would shoot to 14.5 volts.

This is the goal.

Could you check your meter? Like on a another bike or a car or something?
And what does your battery read with the bike OFF?

[manjisann]

The battery reads about 12.4 to 12.7 when off. It's probably not the DMM, more than likely it's the RR, I just want to be sure before I drop the coin on a new RR.

Brandon

[TwoTired]

I'm not all that familiar with the 650's Vreg.  But, I know basically what it should do.
One thing you should do is verify that the Vreg is getting accurate info about the battery's true voltage state.

For example, what if when your battery is at 18V, the regulator only see's 11v of that?  The Vreg thinks the battery is low and tries to charge it up higher.


So compare what the Vreg sees at it's power and ground terminals to what is present at the battery terminals.  Certainly when the Vreg "sees" 18V at it terminals, it should power down the alternator output.

Cheers,

[manjisann]

Ok,  I'm pretty sure the DMM I was using was buggered. Went to Radio Shack and bought a different DMM. I measured the voltage at the battery and at the R/R black and green wire. When the bike was off it was the same, after I had turned the bike on and started and ran her the voltage steadily climbed as the rpms went up. But after about 30 or 40 seconds of running the voltage dropped to below 12 at both the battery and the R/R and there was a difference of .60 volts, the low end being at the R/R. I also noticed this happened as the R/R's back started getting warm. At this point I'm thinking this means the R/R is buggered.

Brandon

[manjisann]

Oh, and I measured for resistance between the battery and R/R and there was none.

Brandon